Servomotor for aircraft controls



Aug. 29, 1950 L, D, CAHlLL ETAL 2,520,115

SERVOMOTOR FOR AIRCRAFT CONTROLS Filed March 30, 1946 4 Sheets-Sheetv 2 All2- 29, 1950 L. D. cAHlLL ETAL 2,520,115

SERVOMOTOR FOR AIRCRAFT CONTROLS Filedl March 30, 1946 4 Sheets-Sheet 5 Aug. 29, 1950 L.. D. CAHILL ET AL SERYQMOTOR FOR AIRCRAFT CONTROLS 4 Sheets-Sheet 4 Filed March 50, 1946 IN VEN TOR. LXSLE D CHM/ 1.

Patented Aug. 29, 1950 SERYOMQf-PQR EDR AIRCRAFT CQNTROLS,

Lysle D. lCahill, South Euclid, and Walter T. Buhl and Alfred S. Horwitz, Shaker Heights, Ohio, assignors to J ack & Heintz Precision Industries, Inc., Cleveland, Ohio, a corporation of Delaware Applicatign March 30, 1946, Serial No.'65,558

This invention relates to servo units for aircraft automatic pilots andv has for one'of its primary objects to provide a self-contained hydraulic servo to include an automaticibuiltdn follow-up system therein.

Another object is to Yprovide an hydraulic servo with a pressure responsive built-in by-pass valve means for engaging and dise'ngag-ing the automatic pilot. v

A further object yis to provide an hydraulic servo with a built-in, s'elf'aligning balanced oil valve means for controlling iiow to and from the motor in the servo. l

Another object is to provide an automatic braking system responsive .to introduction of -fluid pressure to the servo for' causi'riga positive engagement between the'motor and the'main cable drum of the servo.

A further object is to provide in the servo a positive, emergency, v`mechanical disconnect means between the mot'or" and the main cable drum on the servo;

With the foregoing and other objects in view the invention resides in the combination of partis and in the details of constructionset forth in the following specification and appended'cl'aims, certain embodiments thereof being "shown in the ac companying drawings, in whichs' Figure 1 is a View Vin elevation of the servo unit;

Figure 2 is a View in verticalsectio'n of the servo unit;

Figure 3 is a bottom plan View of the b ase of the servo unit with'the cover plate rrenfioved;-

Figure 4 is an enlarged detail View of the bypass oil valve and the balanced oil fvalve shown in Figure 3; Y Y.

Figure 5 is an enlarged detail sectional view taken along 5 5 of Figure 3 showing the fluid passages leading to the bellows; u Figure 6 is an enlarged detail View in section taken along line 6-5 of Figure 4, showing the oil valves;

Figure 7 is an enlarged detail v iew yin section taken along the line 'IQ'I of' Figure 5'; showing the by-pass oil valve;

Figure 8 is an enlarged detail view in section taken along line 8-'8 of vFigure '2, showing the balanced oil Valvef l Y' Figure 9 isa detail View in section taken along linel .9:-9 of Figure 2, showing the hydraulic motor portion of the srvounit;`y Y' Figure 10 is an end view of the servo unit as shown in Figure 1';

Figure. 1l is a View partly in plan and partly in cross section of -theclutch 'or IIHayes Brake 2 portion of the servo unit in its expanded or en gaged position;

' Figure 12 is a view similar to Figure 11, showing the clutch or Hayes Brake in disengaged position;

Figure 13 is an enlarged detail view in section taken along line I3-I3 of Figure 2, showing the mechanical linkage between the clutch or ,vI-Iayes Brake portion of the servo and the drum; and

Figure 14 is an enlarged view in longitudinal section of the metering bushing shown in Figure Referring more particularly to Figure 2 the servo consists essentially of a base I having a cover plate 2, a motor casing 3 and a drum 4. The drum 4 is carried about the motor casing 3 by means .of bearings `5, 6 and 1. The casing 3 is secured to the base I by Vmeans of screws 8 as seen in Figure 1. The cover plate 2 is secured to the base by screws 9. f

In Figure 2 a pressure fluid inlet I ,D is shown on base I leading to a passage Il in the base. Passage I I delivers pressure fluid to a second passage I2 in the housing I3 for 4the by-pass valve 'I4 and the balanced oil valve I5'. `A passage I6 in housing I3 running between and parallel to the valves I4 and' I5 acts as a manifold indelivering pressure fluid from passage I2 to one end of .the valve I4 and to both endsv of valve I5. The passage I2 directs the pressure fluid further into valve I5 by means of a passage I'I Aas shown in Figure 4. The pressure uid remains static about spool IB of valve I 5 between its two central lands I9 and 2!! as long as the aircraft does `not change attitude.' Spool I8 also has end lands 2| and ,'2-2 in sliding engagement with a liner 2 3 in thehousing I3.` The remainderof the valve assemblyv I5 consists of a sleeveV 24 carrying la free sliding piston 25, end caps 25 and A2'I,sump outlets 28 andi29fa metering' needle 3Q and a metering 33 in Fig.` 8to` prevent anyipressure build-ups between itself and the sleeve r24. The metering bushing' 3l is shownin' enlarged detail in Figure Pressure fluid from passage I6 is-directed to the bushing 3| by a'passage 3.4. The bushing directs theiiud into valve I5`between` end land 2 Iv and capV 26. At tliezother end" of valve I5 a passage 35" directs pressure iiuid from .passage .IB to passage36 and into the space between pistonv 25 and cap 2l.v Passage 34 valso directs pressure iiuid from passage I6' to"a passage 3lin valve I4. -ValveIjI has a spool 38 in sliding engagement with a liner against the action of spring 43.

spool I8 in balanced oil valve I5.

Vspool 8 will move to the right.

3s. The Spool 3s which has three lands 4o, 4|

and 42 is held in the position shown in Figure 4 when the automatic pilot is off by action of a compression spring 43 which is held between land 42 and end cap 44. An end cap 45 seals the other end of valve I4, and at the same time provides a protruding stop 46 to engage a stop 41 of spool 38. The stops 46 and 4'| thus provide a limit of travel for spool 38 and make is possible for pressure fluid to be received in valve I4 between land 40 and end cap 45. The valves |4 and I5 are connected by passages 48 and 49 as shown in Figures 7 and 8 and in dotted lines in Figures 4. Passages 48 and 49 also connect with servomotor lines 50 and 5| which are shown in Figure 8 and in dotted lines in Figure 4.

The operation of the valves I4 and I5 is to be considered before continuing with the description of the rest of the servo. With the automatic pilot turned off spool 38 in valve I4 will be in the position shown in Figures 4 and 7. Passages 48 and 49 are open to each other and to both sides of the servomotor, to be discussed later, and consequently the control of the aircraft will be free. Any manipulation of the aircraft control will merely by-passfiuid through valve I4 from one side of the motor to the other.

When the automatic pilot is turned on, the pressure fluid is received in valve |4, as previously described, between land 48 and the end cap 45, forcing spool 38 away from cap 45 The spool 38 will move until the force of the spring equals the force of the pressure fluid which is predetermined to be when land 4| is between the entrances to passages 48 and 49. By moving to this position the spool 38 has cut off the servomotor by-pass and the control will become "locked in whatever position it happens to be.

Meanwhile, simultaneous with the movement of spool 38 is the automatic centralizing of the The centralized or balanced position of the valve is the one in which lands |9 and 29 are directly over passages 48 and 49 as in Figure 8. The position of the spool is controlled at one end by piston 25 and at the other end by metering bushing 3| and needle 38. The linkage controlling the needle movement will be described later. The piston 25 forces the spool I8 toward the needle 30 as pressure uid is received from passage 3B in the sleeve 24. TheY movement of spool I8 by piston 25 is opposed by the build-up of pressure behind land 2| as pressure fluid is received from metering bushing 3|. The needle 3D is moved axially with the spool by its linkage into greater or lesser penetration into chamber 52 in the spool 8, and, in doing so, more or less pressure fluid is allowed to get past insert 53 in land 2| and through the sump passage 54. If in Figure 8 the needle is moved into greater penetration into chamber 52 the If a lesser penetration is effected the spool I8 will move to the left. Although land 2| has four times the cross sectional area that piston 25 does, the ratio between the cross section area at the point of needle penetration into chamber 52 is four to one compared to the smallest inlet area of the metering bushing 3|, so that the relative pressure potential at either end of spool I8 is the same. At the centralized position of the spool I8, the needle 30 is positioned so that 1t is bleeding enough pressure fluid past insert 53 to sump passage 54 to make the forces acting on land 2| and piston 25 equal.

Controlling the movement of the servomotor and consequently the aircraft control with which the servomotor is connected is accomplished by positioning the needle 38 in valve I5. For example, in Figure 8, if the needle is moved further into chamber 52 the force of the pressure fluid on land 2| will increase and overcome the force of the pressure fluid acting on piston 25. The spool I8 will move to the right, and in doing lso will open the line 49 to the high pressure section between lands I9 and 20 of the spool, while at the same time opening line 48 to the sump outlet 28 between lands 2| and I9 of the spool. Since valve |4 has closed the by-pass from passage 49 to passage 48 as previously described, pressure uid will flow from passage 49 into the servomotor by means of passage 5| as shown in Fig. 8. The flow of low pressure fluid from the motor will be through passage 50 to passage 48 and out through sump outlet 28 of the valve I5. If the `needle is moved in the opposite direction the exact opposite of the example just given itrue. Actually the movements of the spool and needle are usually very slight, that is, only enough to actuate the servomotor the amount necessary to give a corrective action to the particular control associated with the motor. A built-in follow-up system, to be discussed later, limits the control action of the servomotor by automatically and simultaneously repositioning the needle to the centralized or balanced position as the control is applied.

The servomotor shown in Figures 2 and 9 consists essentially of the motor casing 3, a stationary vane 55 secured to the casing by bolts 55 and 51, a moving vane 58 and a rotatable shaft 59 mounted on stationary vane and carrying the moving vane. The vanes 55 and 58 have pressure responsixe expandable fluid seals 68, 6| and 82 as described and claimed in a copending application entitled Fluid Seal Serial No. 640,296, now Patent No. 2,466,302 dated April 5, 1949, in the names of Lysle D. Cahill and Roy M. Denham. Pressure fluid is received in seal 68 from a passage 53, shown in Figure 2, which connects directly to passage The seals 6I and SZ-are expanded to rmly engage the casing 3 by means of pressure fluid received from their particular side of vane 58 in passages 54 and 65, respectively. The primary reason for the use of expandable seals is to make a more efficient hydraulic servomotor. The seals 60, 6| and 62 actually act to limit the loss in pressure differential due to leakage from one side of vanes 55 and 58 to the other.

A bushing '66 in base I acts as a bearing for one end of the motor shaft 59. The bushing is provided with a detent 61 for receiving a fluid seal 68 to prevent leakage from the servomotor into the base. A bushing 69 in motor casing cover l0, having detents and 12 to receive fluid seals 13 and '|4,'acts as a bearing for the opposite ends of motor shaft 59. The casing cover 10 is secured to casing 3 by a number of screws 'I5 one of which is shown in Figure 2.

The motor shaft 59 extends out of casing 3 ypast casing cover 'I0 to carry on its extremity a Hayes Brake assembly 16 shown in detail in Figures 11 and 12. The brake is keyed to the shaft 59 by key 'I1 and consists essentially of an outer ring I8 having annular inner surface gear teeth '|9, six gear segments 80 having teeth 8| op- .posite' the teeth 19, a circumferential spring 82 ciarriedin a Adetent'in the vsegr'nerits'l! to .retract the segments vwhen'the automatic pilot 'is off; a pressure responsive expandable rubber e1ement8'4 for carrying .th'e' segments "80,' andtvvo casing members 85 and 8 6." The members 85 and "86 are Vsecured together'by meansof screwsl'l, 88,' 89 and'S'Usho'vv'n in Figure 101 TAne'nd plate 9| is shown in Figures 2' and 1'0' positioned in a recess Pressure iluid is immediately directed to the Clutch," Oi" HayesBrke as autrnatid pilot is'tur'ned"fonby meansofpa'ssages" 32","93; 9E," 93 and 95A asshOWh 'nFigQ 2. Y 'Passage 92is Shown connected" into fixed van@ 55 vbehind "tri egp'and'able fluidseal E0 so as v'to receive pressure rima' therefrom. "Wiienpressufe aciers. riyd the "Hayes Brake gear segments 'BD' areb pushed routwardly Iby'ex'pandable rubber element 'dmuntil the teeth''! engage teeth 'I9 on o uterr'ing' as iri'Figue 1:1. Thus itis seen'tha't anyrnve-` meits'f the Vvs'ervoniotor result in correspond vg Inoi{eh-lents"oil the'houtei` ring F8 when the airori'atic"'piloti"s'\"on. The outer ring '|8 is Connected mechanically with In r1`f`1"'cable"drum 1|v by alink'age having'a'n emergency disconnect "feature This linkage, which is. 'Shown iFsrs 2 10 and' 13, Consists of. a haunting bracket 'er secured a drum my Screwls" andtwo 'parallel ami and. 9.9 tedatbra'cket 9.61611 pivot '|95 and SX# across `the"" H ayesBrake 'to the ODJOSite tf1? @1111.11 The arms 19.31%1159 dci: has@ pice' I D0 as. Shown'i le 1 3 "fio mgmgj a 'suostantiauy U-snapcd member wnichoriiiain seats Snu'giy against nng's be"- twgegn pr raging 'nps mi www2. anpacken |03, Vsecure to dru'4 by. Screws |34, car esa nd'pair'qf' amis" me and mi byjmjns' of M'IT arms, |35. s i'ncilil'ly which funparallel to and'betvveen armsi and' gar'" cnfeced arms, of anni" lo. direct @are the 1p.s'| fl`ai1 d iloithe fine l8- 'lTWO Spacers l l and I| are 'placedY between armsfl@ and |01. The ends of arms |06 and llare forked to receive a pin U24 shown extending through a release lever, |m| 3. The lever ||3 is positioned in a sleeve H llvvithin shaft 5 9, and is held there under the action of a spring ||5 which engages a fork H6 that in turn engages the pin H2. A guide shaft is provided for'the lspring H5. In the 9359.93? @l @..mergffll Wh??? it? Would bf? necessary toprat th'e'emergency disconnect it is merely necessary to pull lever H3. Pulling j|| 3 moves arms |06 andi-B1 by means of a pin ||2. The arms 958m and 99 rare also moved, as arms |03 and |91. Irl-9V?, until. the. has@ hie@ it!! is Completely flies? Q lips.. |91. and |02, O n., rias |8- Thisacton completely frees main cable drum 4 from. any CQIWQOQ With. the Haves Brake and ServomQOr- The spring H holds. the lever :i3 in disengaged, position. just as.. it formerly. held. the.. lever in the. engaged position. Thus it. is Seen that a positive. emergency. disconnect means has. been provided for the servo. unit.

'I he. mechanism for controlling the ultimate mQYements O the. drum 4. by. positioning, needle 3|). in valve |.5 isshovm in Figure '3. Two pressur@ fluid inlets |,8 and U9. are provided in'base to transmit. by, means of. passages |20 and 2| differential pressure signals created by a flight control/unit to a. pair'bfijppo'sed bellows units ure 3 clearly. shows the path of the pressure fluid from inletA I |8 through p'assage |23 and intobellows |22. -Bellows`|22 and |23 are secured to base I by screws 24' and |25, and |25 and "|21, respectively.

A rectangular bracket |28 is positioned so that one side |29 is engaging the opposed ends ci bellows |22 and |23. IPr'otruding from bracketl |28 is a" shaftv |33 which engages an arm |35. lThe arm |31 ispivotally connected at one end to needle 30 by a pivot pin/"|32, and at the other end is pivotal- 1y' connected by pivot pin |33 within the fork shaped end'piece |315 of an arm |35. The end of arm |3| is provided with a counterweight |33. Arm |35 is pivotally carried by a pivot pin |31 bracket |33 vvhichisI secured to base y| 4by a screw |39. A spring MB, secured at one end to a screw |4| in base l" and at the other end to end piece' |34 of arm |35, opposes the action of counterweight |36 and tends to give a counterclockwise movement to the arm 35. A cam iider IU12 is provided on the end of arno |35 to rideon a cam' |43 on the end of motor shaft 59 undery action or? the spring |43. Cam |23 is sec'ured to shaft 59 by means of a Washer- |44 and screvvl.

r`'As-'any differential pressure signal is received bythe bellows |22 and |23 the bracket |28 v vill be moved in the direction of the expansion of the bellows" under greater pressure. Arm |3| and consequently needle 33 are moved accordingly. A s previously described, n ioving 'needl`33 oaus'e's'th spool/w valve -l5 to move ycausing a pressurfluidlow to and from the motor. the rnovingvane 58 andth'inotor shaft 59 are tufnd'to'rotfte the' rnain cable drum il in order to'"get'`the"crrective'control action for the airca`ft`the`cam`|`3 vis also'inoved'. The earn rider |212"T causes 4"arin |35 tore-position the needle 3B to'thebalan'cd `position by means of its linkage withar'm: '|3"|"as"the'control action is applied. In` tl'iis'M Irlannethe built-inA follow-up' action 4of the servo ifs instantaneous vvith'the applied control nelininating the over or vunder control ofthe aircrat'caus'ed by the cable and'pulley follow-up`A systems used 'in former automatic pilot designs. f

"'W fdled from valve through outlets 23'wlfiich completely lubricatesvt'he moving elements in base has a sumpl return outlet |35 in base"|` is shown in Figure 3H.

" althligh Conventional., Safetvfeae Sro, unit' is the inclusion Of two ovrpo evalves |41 andl |443 in fixed vane 5,5 of th'e hydraulic motor portion of the servo. The n l is clearlyshovvn Figure 9v, ist of 'a llioll'ovivf threaded plug |49 holding aball (|59 under compression against the, action @i aSRiaeLiI-ff With. the' automatic pilot Qn the' pfilt'nay .overpower a 'control by exerting enough forc on the control wheel or pedalfto overcome the setting of valver Ifll ori-"lllr. The ffrtedl iS" transmitted. from the 'Qontrol -"le" tomdruin 3, tothe Hayes Brake then to i'. s ad. notre vane c and. muy o 'de' fluid 11.1. casing 3.. When enough force bythe @10i if? orerpoiver the control nm11 |151?. in. relic mi or M5 is unfseated fm'in "inail engagement with, clue ma 'perififit'na flifld lot'. illroush the plus from 011e ide? irai/.ins Varie' 5.3. t@ the. other; the directed 0f '110i' `2|f1sit1 valve @fated Dein?. determined bv fbfdtn flniovnient 0f the van@ itself.;- nFrr'n the foregoing" description of the invention it is seen that a compact servo unit having the features set forth in the objects of :the invention has been provided for use in aircraft hydraulic automatic pilots. It is of course realized that the invention may be headily adapted to other types of hydraulic control systems and to other types of vehicles than aircraft.

We claim:

1. An hydraulic servo unit for use in aircraft automatic pilots for controlling the movements of an aircraft control surface in response to differential signals received from the transmitter of the pilot, comprising an hydraulic fluid displacement motor to actuate said control surface, an inlet for receiving displacement fluid for driving said motor, means to control the displacement fluid flow to and from said motor, and fluid displacement responsive means between said motor and said control surface for causing a positive engagement between said motor and said control surface as said automatic pilot is turned on.

2. An hydraulic servo unit for use in aircraft automatic pilots for controlling the movements of an aircraft control surface in response to differential signals received from the transmitter of the pilot, comprising an hydraulic fluid displacement motor to actuate said control surface, and fluid displacement responsive means between said motor and said control surface for causing a positive engagement between said motor and said control surface as said automatic pilot is turned on Y 3. An hydraulic servo unit for use in aircraft automatic pilots for controlling the movements of an aircraft control surface in response to differential signals received from the transmitter` of the pilot, comprising an hydraulic fluid displacement motor to actuate said control surface, means associated with said motor for receiving said control surface cable, and fluid displacement responsive means between said motor and said control surface for causing a positive engagement between said motor and said control surface as said automatic pilot is turned on and for causing a positive disengagement between said motor and said control surface as said automatic pilot is turned off 4. An hydraulic servo unit for use in aircraft automatic pilots for controlling the movements of an aircraft control surface in response to differential signals received from the transmitter of the pilot, comprising an hydraulic fluid displacement motor for actuating said control surface, a drum mounted on bearings about said motor for connection to said control surface and a hydraulically actuated clutch system between said motor and the drum for causing a positive engagement between said motor and said drum as said automatic pilot is turned on and for causing a positive disengagement between said motor and said drum as said automatic pilot is turned olf 5. An hydraulic servo unit for use in aircraft automatic pilots for controlling the movements of an aircraft control surface in response to differential signals received from the transmitter of the pilot, comprising an hydraulic fluid displacement motor` for actuating said control surface, fluid displacement responsive means between said motor and said control surface for causing a positive engagement between said motor and said control surface as said automatic pilot is turned on, and manual means for positively disengaging said motor from said control surface.

6. An hydraulic servo unit for use in aircraft automatic pilots for controlling the movements of an aircraft control surface in response to differential signals received from the transmitter of 'the pilot, comprising an hydraulic fluid displacement motor for actuating said control surface, a, drum mounted on bearings about said motor for connection to said control surface, a hydraulically operated clutch system between said motor and said control surface for causing a positive engagement between said motor and said control surface as said automatic pilot is turned on and for causing a positive disengagement between said motor and said control surface as said automatic pilot is turned offf and a manual emergency mechanical means for positively disconnecting said clutch system from the drum when said automatic pilot is off, or on.

7. An hydraulic servo unit for use in aircraft gyroscopic automatic pilots for controlling the movements of an aircraft control surface in response to differential signals received from the transmitter of the pilot, comprising an hydraulic fluid displacement motor for actuating said control, a self-balancing oil valve for controlling displacement fluid flow to said hydraulic motor, a pair of opposed displacement responsive bellows linked to said oil valve for regulating said valve in response to differential signals from said gyroscopic pilot for determining the direction of movement of said motor, a follow-up system associated with said motor and with said balanced oil valve for limiting the movement of said motor in proportion to the regulation applied by said bellows to said oil valve, a drum mounted on bearings about said motor for connection to the control surface, a hydraulic clutch system between said motor and said drum for causing a. positive engagement between said motor and said drum as said automatic pilot is turned on and for causing a positive disengagement between said motor and said drum as said automatic pilot is turned off and a manual emergency mechanical means for positively disconnecting said clutch system from said drum when said automatic pilot is off or on.

LYSLE D. CAHILL. WALTER rr. BUHL. ALFRED s. HoRWrrz.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 1,938,338 Jirnerson Dec. 5, 1933 2,179,179 Fischel Nov. 7, 1939 2,225,321 Schwendner Dec. 17, 1940 2,226,191 Alkan Dec. 24, 1940 2,227,375 Carlson Dec. 31, 1940 2,245,562 Becker June 18, 1941 2,342,184 Fawcett Feb. 22, 1944 2,348,768 Warner May 16, 1944 2,356,597 Kronenberger Aug. 22, 1944 2,358,845 Alexanderson Sept. 26, 1944 2,372,710 Chisholm Apr. 3, 1945 2,390,119 Nisbet Dec. 4, 1945 2,453,650 Alexanderson Nov. 9, 1948 FOREIGN PATENTS Number Country Date 217,121 Switzerland Feb, 16, 1942 

